题目

Ice FishingDear members,I’m excited about this Sunday’s ice fishing. We are to meet at 9:00 am and then take the bus to the lake.Please arrive on time. Before you set off, here is some advice for you:● Wear the right clothes. You should dress in layers (层). Wear two or three shirts, so you can take off a layer when you are warm. Wear a face mask, a warm hat and gloves.● Stay warm. Be sure to take a hot drink, for example a hot chocolate. You should move around to stay warm. Some people take ice-skates.● Check the ice. Look at it carefully. The ice must be 10 cm or more thick. Thick抛掷一枚硬币，规定正面向上得1分，反面向上得-1分，则得分X的均值与方差分别为   [     ]A．E （X ）=0 ，D （X ）=1B．C．E（X）=0，D．